Circuits are known for testing control selector switches in a telephone switching system. An example of such a tester is disclosed in U.S. Pat. No. 3,627,932. However, such testers, though desirably arranged for testing proper operating conditions of the trunk circuits accessed by the control selector switch to which the test set is connected, cannot be used for sequencing and testing forward selector switches in the telephone system.
Additionally, telephone systems have a control relay for causing completion of a trunk circuit and for forming dial pulses in the telephone system. The control relay is generally known as the A relay. Prior dynamic testers have not had any way of testing to determine when the A relay is marginal, i.e., does not operate properly when marginally low values of current are applied, but which will pulse the A relay with a high value of current sufficient to ensure its proper operation for providing dial pulses forward to other switches in the system.